Force-measuring apparatus for use in a well bore pipe string

ABSTRACT

In the representative embodiment of the apparatus of the present invention disclosed herein, a force-responsive sleeve is coaxially mounted around and secured at its opposite ends to a tubular body so that, when the body is coupled into a well bore pipe string, only a minor portion of any torsional or longitudinal forces acting on the body will be proportionally imposed on the sleeve. To greatly enhance the effects of these forces, the sleeve is normally maintained in longitudinal tension and a short central portion thereof is significantly reduced in cross-section. One or more arrays of strain gages mounted on the reduced portion of the sleeve are cooperatively arranged for providing electrical signals which are representative of the longitudinal and torsional forces imposed on the body tending to dimensionally distort the reduced sleeve portion. The effects of pressure differentials between fluids interior and exterior of the tubular body are eliminated by mounting an expansible protective sleeve around the body to define an enclosed annular space around the force-responsive sleeve that is communicated with a pressure-balancing piston in the body for equalizing the pressures in the annular space and the interior bore of the body.

tinned States harem FORCE-MEASURING APPARATUS F OR USE IN A WELL BORE PIPE STRING Inventor: Jackson R. Claycomb, Houston,

' Tex.

[73] Assignee: Schlumberger Technology Corporation, New York, NY.

Filedt Nov. 19 1973 Appl. No.: 417,006

Related U.S. Application Data Division of Ser. No. 358,562, May 9, 1973.

US. Cl. 73/151, 73/133 R int. Cl E2lb 47/00 Field of Search 73/151, 133 R, 141 A, 136 A,

[5 6] References Cited UNITED STATES PATENTS 1/1949 Ruge 73/14] A 4/1949 Mathews 73/141 A X 11/1965 Golding 1 73/88.5 R X 8/1972 Chatard et al. 73/151 4/1974 Tveter 73/136 A Primary Examiner-Jerry W. Myracle Attorney, Agent, or Firm'-Ernest R. Archambeau, Jr.; William R Sherman; Stewart F. Moore [451 Dec. 24, 1974 [57] ABSTRACT In'the representative embodiment of the apparatus of the present invention disclosed herein, a forceresponsive sleeve is coaxially mounted around and secured at its opposite ends to a tubular body so that, when the body is coupled into a well bore pipe string, only a minor portion of any torsional or longitudinal forces acting on the body will be proportionally imposed on the sleeve. To greatly enhance the effects of these forces, the sleeve is normally maintained in longitudinal tension and a short central portion thereof is significantly reduced in cross-section. One or more arrays of strain gages mounted on the reduced portion of the sleeve are cooperatively arranged for providing electrical signals which are representative of the longitudinal and torsional forces imposed on the body tending to dimensionally distort the reduced sleeve por- -tion. The effects of pressure differentials between fluids interior and exterior of the tubular body are eliminated by mounting an expansible protective sleeve around the body to define an enclosed annular space around the force-responsive sleeve that is communicated with a pressure-balancing piston in the body for equalizing the pressures in the annular space and the interior'bore of the body,

31 Claims, 2 Drawing Figures PAIEmmnEtw 3.855.857

F SIGNAL ,6 I DETECTOR 5 GENERATOR CONDITION MEASURING I DEVICES FORCE Y 19220 RESPONS/VE MEANS 17 F 5 2 FORCE-MEASURING APPARATUS FOR USE llN A WELL BORE PIPE STRING This application is a division of my copending application Ser. No. 358,562, filed May 9, 1973 for Well Bore Force-Measuring Apparatus.

Those skilled in the art will, of course, appreciate that it is of great value to know the axial load as well as the applied torqueon the drill bit during the drilling of a well. In addition to being useful in controlling the direction or inclination of the borehole as it is being drilled, such measurements are also of great significance in achieving the most efficient and economical drilling program for that well. For example, it is a common practice to pre-schedule the drilling program for a given well so that the most efficient drilling speeds, bit loads, and drill bits will be used for drilling each of the several formation intervals which are expected to be encountered before the borehole reaches its specified depth.

Heretofore, many long-standing techniques have been employed for either estimating or empirically measuring the bit torque and weight-on-bit from the surface. Those skilled in the art will, of course, recognize that any surface measurements which of necessity must be extrapolated to derive an assumed bit torque or weight-on-bit are subject to many potential errors arising from such factors as the friction of the drill string against the borehole wall. Accordingly, it is widely recognized that knowledge with a fair degree of precision of the actual weight-on-bit and bit torque at any given time during a typical drilling operation is of far greater benefit than simply estimating these loads to optimize such operations.

To obtain measurements representative of the actual weight-on-bit load as well as the bit torque, various force-measuring devices have been previously proposed for use with different types of signaling systems such as the downhole signaling systems shown in U.S. Pat. No. 3,736,558 or U.S. Pat. No. 3,764,970 for transmitting encoded acoustic data signals to the surface through the circulating mud stream in the drill string. One of the more common of these forcemeasuring devices employs an array of suitable strain gages mounted on one of the several conventional drill collars which are customarily connected'in a typical drill string immediately above the drill bit. Those skilled in the art will recognize, however, that such arrangements are essentially so insensitive that only major changes in the load conditions can be detected. Quite simply, the problem is that with the typical heavy-walled drill collars used in present-day drilling operations, the amount of deformation experienced thereby in response to changes in either torsional or axial loadings are so minute that even the most sophisticated strain gages will simply fail to adequately respond.

To counter these major disadvantages, various proposals have been made for increasing the output responseof such strain gages. For example, as shown in FIG. 3 of U.S. Pat. No. 2,422,806, a conventional force-responsive transducer is mounted on an upright post and this assembly is mounted between two opposed shoulders defined by a shallow recess in the wall of a drill collar to provide output signals representative of the deformations of the slightly-reduced wall section. Although this arrangement ofiers slightly more sensitivity, the degree of deformation in this wall'section which might ordinarily occur during a typical drilling operation is nevertheless so extremely small that the resulting output measurements are still somewhat insensitive to anything short of significant changes in the load conditions on the drill bit.

An alternative proposal is found in U.S. Pat. No. 3,686,942 in which an independent load-bearing member carrying an array of strain gages is cooperatively telescoped within a stronger load-bearing member and arranged to carry all of the axial and torsional loads acting on the drill bit so long as these loads remain within a predetermined range which is well within the useful strength of the weaker transducer-bearing member. Should, however, the loads on the drill bit exceed the maximum design capabilities of the transducerbearing member, the weaker load-carrying member will be moved into engagement with a cooperative shoulder on the stronger load-carrying member so that the entire load will thereafter be imposed on this paralleling member thereby relieving the weaker member of these potentially-damaging loads. Although this particular arrangement offers many advantages not found heretofore, those skilled in the art will recognize, nevertheless, that since this transducer-bearing member muststill be capable of supporting significant axial or torsional loads, the strain gages will still be relatively insensitive to minor load'changes.

Accordingly, it is an object of the present invention to provide new and improved force-measuring apparatus for reliably providing accurate measurements of even minor axial or torsional loads which may act on a well bore pipe string such as those imposed on a drill string during the course of a drilling operation.

This and other objects of the present invention are attained by securing the opposite ends of a pretensioned elongated force-responsive member to spaced locations on a tubular load-bearing body which is adapted for coupling into a string of well pipe such as a drill string. A minor portion of the force-responsive member is greatly reduced in cross-sectional area and one or more force-responsive transducers are cooperatively secured to this greatly-reduced portion. In this manner, upon application of any load on the loadbearing body tending to change the tension normally existing in the force-responsive member, even minute load-induced deformations of the load-bearing body will induce greatly-increased proportional tensile variations or dimensional deformations in the reduced portion of the force-responsive member for producing correspondingly-enhanced output signals from the transducers. To protect the sensitive force-measuring elements in the new and improved apparatus of the present invention from high pressure differentials which typically occur in a well bore, a protective longitudinally-expansible tubular member is arranged around the load-bearing body to dispose the-forceresponsive member with an enclosed space and pressure-equalizing means are cooperatively arranged for maintaining the space at an elevated pressure such as principles of the present invention as illustrated in the accompanying drawings, in which:

FIG. 1 shows new and improved force-measuring apparatus employing the principles of the present invention as it will appear while arranged in a drill string during the course of a typical drilling operation; and

FIG. 2 is an enlarged view of the preferred embodiment of the force-measuring apparatus shown in FIG. 1.

Turning now to FIG. 1, a downhole data-signaling well tool such as either of those shown in U.S. Pat. No. 3,736,558 or U.S. Pat. No. 3,764,970 is depicted coupled to the lower end of a typical drill string 11 made up of a plurality of pipe joints 12 and one or more drill collars l3 and having a rotary drill bit 14 dependently coupled thereto for excavating a borehole 15 through various earth formations as at 16. As the drill string 11 is rotated by a typical drilling rig (not shown) at the surface, substantial volumes of the drilling fluid or so-called mud" are continuously pumped downwardly through the tubular drill string and the tool 10 and discharged from the drill bit 14 for cooling the bit as well as carrying borings removed by the bit to the surface as the mud is returned upwardly along the borehole 15 exterior of the drill string. As is typical, the mud stream is circulated by employing one or more high-pressure mud pumps (not shown) which continuously draw the fluid from a storage bit or surface vessel (not shown) for subsequent recirculation by the mud pumps. It will be appreciated, therefore, that the circulating mud stream flowing through the drill string 11 serves as a transmission medium that is well suited for transmitting acoustic data signals from the datasignaling tool 10 to the surface at the speed of sound in the particular drilling fluid.

In accordance with the principles of the present invention, new and improved force-measuring apparatus 17 is preferably arranged in the drill string 11 between the well tool 10 and the bit 14 and electrically coupled to appropriate measurement encoder means 18 operatively arranged in the data-signaling tool for producing a series of electrical coded data signals that are representative-of the forces being imposed on the drill bit. It will, of course, be appreciated that the data-signaling tool 10 can also be coupled to one or more conditionresponsive devices, as at 19 and 20, cooperatively arranged on the tool for measuring such downhole conditions as the pressure, the temperature, or the resistivity or conductivity of either the drilling mud or the adjacent earth formations as well as various formation conditions or characteristics which are typically obtained by variouscommercial logging tools. These conditionmeasuring devices 19 and 20 are also cooperatively coupledto the measurement encoder 18 for independently producing electrical signals that are each representative of the particular downhole conditions or formation properties which are being measured. It will be understood, of course, that the measurement encoder 18 will be cooperatively arranged so as to sequentially obtain each of the several desired measurements for independently transmitting a representative encoded signal to the surface. Although a self-contained battery or power supply can be employed, as shown at 21 it is preferred to employ a reaction-type turbine driving a generator for utilizing the circulating mud stream passing through the tool 10 as a motivating source to generate electrical power for operation of the tool.

The data-signaling tool 10 is preferably arranged as described in greater detail in U.S. Pat. No. 3,764,970 which is incorporated by reference herein. As described in that patent, the tool 10 includes a signaltransrnitting unit 22 having an electric motor 23 which is coupled by control circuitry 24 to the encoder l8 and operatively arranged to respond to its coded output signals for rotatively driving an acoustic signaler 25 by way of a typical gear train 26 to successively interrupt or obstruct the flow of mud through the drill string 11. The resulting acoustic signals produced by the acoustic signaler 25 will be successively transmitted to the surface through the mud stream flowing within the drill string 11 as sequential encoded data signals indicative of the force measurements provided by the forceresponsive apparatus 17 as well as the one or more downhole conditions or formation characteristics respectively sensed by the condition-measuring devices 19 and 20. As these acoustic data signals are successively transmitted to the surface, they are detected and converted into meaningful indications or records by suitable acoustic signal detecting-and-recording apparatus 27 such as disclosed in either US Pat. Nos. 3,309,656, 3,488,629, 3,555,504, or 3,716,830, or 3,747,059, each of which are incorporated by reference herein. It will, of course, be further recognized that the acoustic signaler 25 could also just as well be the signaler described in either U.S. Pat. Nos. 3,764,968 or 3,764,969, each of which are incorporated by reference herein. Similarly, the signaltransmitting unit 22 could be any of the new and improved downhole units described in either U.S. Pat. Nos. 3,309,656, 3,711,825, 3,713,089 or 3,763,558, each of which are incorporated by reference herein.

Turning now to FIG. 2, a cross-sectioned elevational view is shown of a preferred embodiment of the forceresponsive apparatus 17. As seen there, the forceresponsive apparatus 17 preferably includes a thickwalled tubular sub or body 28 which is cooperatively arranged in a typical manner with appropriate end connections, as at 29 and 30, to allow the sub to be tandemly coupled at a desired location in the drill string 11. The sub 28 includes an axial fluid passage 31 for conducting the drilling fluid flowing through the drill string 11 to the drill bit 14 therebelow. Although the tubular body 28 could be arranged to have an external diameter substantially equal to the external diameter of the adjacent body 13 of the tool 10, it is preferred to moderately reduce the external diameter of the central portion of the tubular sub so as to leave a reduceddiameter thick-walled portion, as at 32, of sufficient thickness and strength to withstand the rigorous loads normally experienced during the drilling of a typical well bore. For reasons which will subsequently be explained in greater detail, it will be appreciated that the overall length or longitudinal dimensions of the reduced-diameter portion 32 is preferably a substantial percentage of the overall length of the tubular body 28.

diameter intermediate portion 32. It will be recognized, of course, that as compressive forces are axially applied on the tubular body-28, its overall length will be proportionally shortened in direct relation to the magnitude of the compressive load. Thus, inasmuch as the thin-walled sleeve 33 is rigidly secured at its upper and lowerv ends to the end portions 36 and 37 of the tubular body 28, any deformation acting on the body will be correspondingly transferred directly to the sleeve. In other words, if a given axial load is sufficient to shorten the tubular body 28 by O. 1-inch, for example, the thinwalled sleeve 33 must also be shortened by 0.1-inch.

Accordingly, in keeping with the objects of the present invention, the mid-portion 38 of the thin-walled sleeve 33 is significantly reduced in diameter so as to define a very thin wall which is extremely shorter than the overall length of the sleeve. Furthermore, by making the thickness of the short mid-portion 38 of the sleeve 33 significantly less than the thickness of the end portions 39 and 40 of the thin-walled sleeve, it will be appreciated that these thicker portions will be substantially stiffer than the thin mid-portion so that the large or major portion of any total axial deformation acting on the sleeve will be accommodated by or concentrated in this mid-portion. Thus, for a given axial force and the resulting longitudinal deformation of the loadbearing tubular body 28, most, if not all, of the corresponding deformation which must take place along the length of the thin-walled sleeve 33 will be concentrated in the relatively short length of the reduced-diameter mid-portion 38 of the sleeve. Simple mathematical analysis will, of course, show that the amount of deformation which will be experienced by the very thin midportion 38 of the sleeve 33 will be proportional to the ratio of the thicknesses of the remaining portions 39 and 40 of the sleeve and this thinner portion as well as the ratio in the length of the center portion of the overall length of the thin-walled sleeve. Those skilled in the art will appreciate, therefore, that a substantial deformation will be experienced in this thin mid-portion 38 of the sleeve 33 even under relatively minor axial loads on the tubular body 28 causing only a very minor deformation which must be distributed uniformly along the full length of the tubular body. It may be said, therefore, that this unique arrangement provides a significant amplification of the amount of deformation which will be experienced by the thin mid-portion 38 of the sleeve 33 and thereby cause a much greater range of longitudinal deformation or movement at this location than will be realized at any other portion of the new and improved force-measuring apparatus 17. Accordingly, for measuring axial loads on the drill bit 14, force-responsive transducer means such as one or more typical strain gages 41 and 42 are mounted at spaced intervals around the circumference of the reduced midportion 38 of the sleeve 33 for providing significant output signals in. response to even minor axial deformations of the load-bearing sub 28. Suitable provisions are, of course, made for electrically connecting the transducers 41 and 42 to the encoder 18.

It will be recalled that the sleeve 33 is cooperatively secured to the tubular body 28 so as to normally maintain the thin-walled sleeve in tension even when there are no forces imposed on the body. Inasmuch as neither the end portions 39 and 40 of the thin-walled sleeve 33 nor its greatly-reduced mid-portion 38 are capable of withstanding axial or compressive forces of any consequence, it will be recognized that by maintaining the thin-walled sleeve in tension, its reduced-thickness mid-portion will not be subject to collapse as axial loads are applied to the force-measuring apparatus 17. Instead, as axial compressive loads are applied to the new and improved force-measuring apparatus 17, the tensile forces acting on the thin-walled sleeve 33 will simply be reduced in magnitude and cause its midportion 38 to contract. Conversely, reduction of these axial compressive loads will simply elongatethe midportion 38 of the sleeve 33 in proportion to the change 'in applied load.

To provide the most fool-proof arrangement of the new and improved apparatus 17, it is preferred that the thin-walled sleeve 33 be tensioned to approximately half of its yield strength. In this manner, tensile forces such as might be imposed upon bending of the forcemeasuring apparatus 17 will only result in further elongation of the mid-portion 38 of the force-measuring sleeve 33 and axial compressive loads on the forcemeasuring tool will merely reduce the tensile forces on eration. Accordingly, to arrange the force-measuring apparatus 17 for also monitoring torsional forces acting on the drill bit 14, torque-responsive transducer means such as one or more typical strain gages, as at 43 and 44, are mounted in sets at spaced circumferential intervals around the reduced-thicknessmid-portion 38 of the thin-walled sleeve 33. By arranging each of these transducers 43 and 44 at an angle of approximately 45 to the longitudinal axis 45 of the force-measuring apparatus I7 and at right angles to one another, those skilled in the art will appreciate that the resulting measurements will be representative of the torsional forces acting at any time on the force-measuring apparatus. Hereagain, inasmuch as the thickness of the reduced mid-portion 38 is substantially less than that of the end portions 39 and 40 of the thin-walled sleeve 33, torsional forces acting thereon will be substantially concentrated at the reduced wall portion. In this manner,

as previously mentioned with reference to the axial compressional forces, the output signals provided by the torque-responsive strain gages 43 and 44 will be greatly increased over what would otherwise be provided if it were not for the particular unique arrangement of the present invention.

The various devices used heretofore for measuring torque and weight-on-bit have typically either ignored or taken less than adequate measures for limiting or avoiding the effects of pressure differentials which must otherwise affect the accuracy of the force measurements. Those skilled in the art will, of course, appreciate that there is normally a substantial pressure differential between the drilling fluid flowing through the drill string 11 and the pressure in the borehole 15 exterior of the drill string. Where there are downhole signaling devices such as those previously described herein for transmitting acoustic signals to the surface,

the additional restriction provided by these signaling devices will also significantly increase the pressure differential acting across the force-measuring apparatus 17. Thus, if no preventative measures are taken for protecting or isolating the thin-walled sleeve 33, an increased pressure in the longitudinal bore 31 would tend to circumferentially enlarge as well as elongate the tubular body 28 and thereby impose a corresponding deformation on the reduced-thickness sleeve portion 38 which, unless properly compensated, would result in an unwanted signal output from the several transducers, as at 41-44.

Accordingly, to provide for such isolation, a thickwalled tube 46 is coaxially mounted around the thinwalled sleeve 33 and secured at its upper end to the tubular body 28 by means such as threads 47 and sealed as at 48. Instead of securing the lower end of the thickwalled tube 46 to the tubular body 28, its lower end is inwardly enlarged, as at 49, and provided with a fluid seal 50 for defining an enclosed annular space 51 around the thin-walled sleeve 33. To maintain the annular space 51 at a pressure which will minimize or eliminate circumferential expansion of the tubular body 28 due to pressure differentials, the annular space is filled with a suitable hydraulic fluid, such as oil, and pressure-balancing means, such as a piston 52 mounted in a cylinder 53 in the wall of the tubular body and coupled by a passage 54, are provided for communicating the pressure of the drilling mud flowing through the internal bore 31 to the annular space. To allow the oil filling the annular space 51 to communicate with both sides of the force-measuring sleeve 33, one or more ports 55 are formed in the thin-walled sleeve. In this manner, it will be appreciated that the oil filling the annul-ar space 51 will be maintained at a pressure equal to that of the drilling fluid flowing through the longitudinal bore 31.

Those skilled in the art will, of course, also recognize that with a number of transducers, as at 41 and 42, distributed around the reduced mid-portion 38 of the sleeve 33, measurements can also be obtained which are representative of the degree of any axial bending of the total body 28. In other words, since axial bending of the body 28 will place one side of the body in tension and the other side of the body in compression, transducers, as at 41 and 42, on opposite sides of the midportion 38 will individually provide output signals representative of the forces. By separately measuring these forces on opposite sides of the tool body 28 the extent of bending can, of course, be readily determined.

It should also be noted that by leaving the lower end of the thick-walled tube 46 free to move in relation to the tubular body 28, any pressure or thermal conditions which would otherwise tend to deform the thick-walled tube and thereby change the pressure in the annular space 51 will instead be accommodated by movement of the lower end of the tube in response to these conditions.

Accordingly, it will be appreciated that the new andimproved force-measuring apparatus 17 of the present invention is particularly responsive to both axial and torsional forces for producing much-greater output signals than has ever been possible heretofore. By arranging the force-responsive sleeve 33 to be particularly susceptible to pronounced or magnified deformation at the very location of the several strain-measuring devices as at 41-44, the typical low outputs of these devices will be greatly accentuated so as to provide a much wider proportional band or response than would otherwise be possible. Moreover, by placing the forceresponsive sleeve 33 in tension as previously described, there is no concern that this weak force-responsive sleeve will be damaged by even extreme axial or torsional loads. Moreover, by arranging the forcemeasuring apparatus 17 to be pressure balanced, the effects of changes in temperature or pressure that would otherwise tend to limit the reliability and accuracy of the force measurements are obviated.

While only a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Apparatus adapted for sensing loads acting on a string of pipe in a well bore and comprising:

a load-bearing body adapted for coupling between adjacent sections of a pipe string;

an elongated load-responsive member having opposite end portions respectively secured to spaced portions of said load-bearing body and cooperatively arranged for normally maintaining said lead responsive member in tension and an unrestrained intermediate portion adapted to contract and elongate in response to increases and decreases in loads imposed on said load-bearing body tending to move said spaced body portions in relation to one another; and

transducer means coupled to said intermediate portion of said load-responsive member and having a measurable characteristic adapted for varying in response to changes in the tensile forces in said load-responsive member occurring upon relative movement between said spaced body portions.

2. The load-sensing apparatus of claim 1 wherein said spaced portions of said load-bearing body are longitudinally spaced from one another so that changes in axial loads imposed on said load-bearing body will change the tensile forces in said load-responsive member as said spaced body portions move longitudinally in relation to one another.

3. The load-sensing apparatus of claim 1 wherein said spaced portions of said load-bearing body are longitudinally spaced from one another and normally angularly aligned so that changes in axial loads imposed on said load-bearing body will change the tensile forces in said load-responsive member as said spaced body portions move longitudinally in relation to one another and changes in torsional loads imposed on said load-bearing body will change the tensile forces in said loadresponsive member as said spaced body portions move angularly in relation to one another.

4. The load-sensing apparatus of claim 1 wherein said measurable characteristic is an electrical property; and said transducer means include at least one strain gage mounted on said intermediate portion of said loadresponsive member and exhibiting a varying range of said electrical property in response to tension variations in said load-responsive member.

5. The load-sensing apparatus of claim 1 wherein said load-responsive member is normally tensioned to about half of its rated yield point.

6. Apparatus adapted for sensing loads acting on a string of pipe in a well' bore and comprising:

a load-bearing body adapted for tandem coupling in a pipe string;

an elongated load-responsive member having opposite end portions respectively secured to spaced portions of said load-bearing body for normally maintaining said load-responsive member in tension and-a reduced-thickness intermediate portion adapted to deform in response to loads imposed on said load-bearing body tending to move one of said spaced body portions in relation to the other of said spaced body portions; and

transducer means coupled to said reduced-thickness portion of said load-responsive member and having a measurable characteristic which varies in relation to variations in the tension in said load-responsive member occurring upon relative movement be tween said spaced body portions.

7. The load-sensing apparatus of claim 6 wherein said load-responsive member is normally tensioned to about half of its rated yield point.

8. The load-sensing apparatus of claim 6 wherein said measurable characteristic is an electrical property; and said transducer means include at least one strain gage mounted on said reduced-thickness portion of said load-responsive member and exhibiting a varying range of said electrical property in response to tension variations in said load-responsive member.

9. The load-sensing apparatus of claim 6 wherein said opposite end portions of said load-responsive member are spaced longitudinally from one another so that changes in axial loads imposed on said load-bearing body will cause said load-responsive member to proportionally contract and elongate as such axial loads increase and decrease; and said transducer means include at least one tension-responsive strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to contraction and elongation of said load-responsive member.

10. The load-sensing apparatus of claim 6 wherein said opposite end portions of said load-responsive member are angularly aligned and spaced longitudinally from one another so that changes in torsional loadsimposed on said load-bearing body will cause said load-responsive member to proportionally twist and untwist as such torsional loads increase and' decrease; and said transducer means include at least one strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to variations in the torsional forces acting on said load-responsive member.

11. The load-sensing apparatus of claim 6 wherein said opposite end portions of said load-responsive member are angularly aligned and spaced longitudinally from one another so that changes in torsional loads imposed on said load-bearing body will cause said load-responsive member to proportionally twist and untwist as such torsional loads increase and decrease and changes in axial loads imposed on said load bearing body will cause said load-responsive member to proportionally contract and elongate as such axial loads increase and decrease; and said transducer means include at least a first strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to variations in the torsional forces acting on said load-responsive member'and at least a second strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to variations in the tensile forces acting on said load-responsive member upon contraction and elongation of said load-responsive member.

12. The load-sensing apparatus of claim 6 wherein said load-responsive member is exterior of said loadbearing body.

13. The load-sensing apparatus of claim 12 wherein said load-responsive member is tubular and is coaxially arranged on said load-bearing body.

14. The load-sensing apparatus of claim 12 further including:

a sleeve member cooperatively arranged around said load-responsive member and having upper and lower end portions respectively extending above and below said spaced portions of said load-bearing y;

first and second means respectively fluidly sealing said upper and lower end portions of said sleeve member to said load-bearing body for defining an enclosed chamber around said load-responsive member; and

pressure-regulating means cooperatively arranged on said body and adapted for maintaining said enclosed chamber at an elevated pressure.

15. The load-sensing apparatus of claim 14 wherein said load-responsive member is tubular and is coaxially arranged on said load-bearing body within said enclosed chamber.

16. Apparatus adapted for sensing loads acting on a drill bit dependently coupled to a drill string and operatively arranged for excavating a borehole and comprisa load-bearing body adapted for being tandemly coupled between a drill bit and a tubular drill string section and having a longitudinal bore adapted for conducting drilling fluids therebetween;

a load-responsive sleeve coaxially arranged on said load-bearing body and having upper and lower end portions respectively secured rigidly to longitudinally-spaced upper and lower portions of said loadbearing body for normally maintaining said loadresponsive sleeve in tension; and 1 electrical transducer means cooperatively arranged on an unrestrained intermediate portion of said load-responsive sleeve and adapted for exhibiting a varying electrical characteristic proportional to changes in the tension in said load-responsive .sleeve occurring upon variations in loads acting on said load-bearing body.

17. The load-sensing apparatus of claim 16 further including:

means on said load-responsive sleeve cooperatively arranged for concentrating strain in said unrestrained sleeve portion upon changes in the tension occurring in said load-responsive sleeve.

18. The load-sensing apparatus of claim 16 wherein said load-responsive sleeve is exterior of said loadbearing body.

19. The load-sensing apparatus of claim 18 further including:

a tubular housingcooperatively arranged around said load-responsive. sleeve;

lll

first and second means respectively fluidly sealing the upper and lower end portions of said tubular housing to said load-bearing body above and below said load-responsive sleeve for defining an enclosed chamber therearound; and

pressure-equalizing means on saidd load-bearing body and cooperatively arranged for maintaining said enclosed chamber at a pressure at least about equal to the pressure in said longitudinal bore.

20. The load-sensing apparatus of claim 16 wherein said electrical transducer means include:

at least one tension-responsive strain gage mounted on said unrestrained portion of said loadresponsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body.

21. The load-sensing apparatus of claim 16 wherein said electrical transducer means include:

at least one set of tension-responsive strain gages mounted on said unrestrained portion of said loadresponsive sleeve and cooperatively arranged for responding to angular twisting and untwisting of said load-responsive sleeve caused by changes in torsional loads imposed on said load-bearing body.

22. The load-sensing apparatus of claim 21 wherein said electrical transducer means further include:

at least one tension-responsive strain gage mounted on said unrestrained portion of said loadresponsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body.

23. Apparatus adapted for sensing loads acting on a drill bit dependently coupled to a drill string and operatively arranged for excavating a borehole and comprising:

a tubular load-bearing body having upper and lower ends respectively adapted for coupling said body in a drill string and a longitudinal bore adapted for conducting drilling fluids flowing therefrom to a drill bit coupled therebelow;

a load-responsive sleeve coaxially arranged around said load-bearing body and having a reducedthickness intermediate portion between upper and lower portions of said load-responsive sleeve;

means rigidly securing said upper and lower portions of said loadresponsive sleeve respectively to longitudinally-spaced portions of said load-bearing body for normally maintaining said intermediate portion of said load-responsive sleeve in tension; and

electrical transducer means cooperatively arranged on said intermediate portion of said loadresponsive sleeve and adapted for exhibiting a varying electrical characteristic proportional to changes in the tension in said load-responsive sleeve occurring upon variations in loads acting on said load-bearing body.

24. The load-sensing apparatus of claim 23 wherein said electrical transducer means include:

at least one tension-responsive strain gage mounted on said intermediate portion of said loadresponsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body. 25. The load-sensing apparatus of claim 23 wherein said electrical transducer means include:

at least one set of tension-responsive strain gages mounted on said intermediate portion of said loadresponsive sleeve and cooperatively arranged for responding to angular twisting and untwisting of said load-responsive sleeve caused by changes in torsional loads imposed on said load-bearing body.

26. The load-sensing apparatus of claim 25 wherein said electrical transducer means further include:

upper and lower end portions of said tubular housing to said load-bearing body above and below said load-responsive sleeve for defining an enclosed chamber therearound; and

pressure-equalizing means on said load-bearing body and cooperatively arranged for maintaining said enclosed chamber at a pressure at least about equal to the pressure in said longitudinal bore. 29. The load-sensing apparatus of claim 28 wherein said electrical transducer means include:

at least one tension-responsive strain gage mounted on said intermediate portion of said loadresponsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body. 30. The load-sensing apparatus of claim 28 wherein said electrical transducer means include:

at least one set of tension-responsive strain gages mounted on said intermediate portion of said loadresponsive sleeve and cooperatively arranged for responding to angular twisting and untwisting of said load-responsive sleeve caused by changes in torsional loads imposed on said load-bearing body.

31. The load-sensing apparatus of claim 30 wherein said electrical transducer means further include:

at least one tension-responsive strain gage mounted on said intermediate portion of said loadresponsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body. 

1. Apparatus adapted for sensing loads acting on a string of pipe in a well bore and comprising: a load-bearing body adapted for coupling between adjacent sections of a pipe string; an elongated load-responsive member having opposite end portions respectively secured to spaced portions of said load-bearing body and cooperatively arranged for normally maintaining said load-responsive member in tension and an unrestrained intermediate portion adapteD to contract and elongate in response to increases and decreases in loads imposed on said load-bearing body tending to move said spaced body portions in relation to one another; and transducer means coupled to said intermediate portion of said load-responsive member and having a measurable characteristic adapted for varying in response to changes in the tensile forces in said load-responsive member occurring upon relative movement between said spaced body portions.
 2. The load-sensing apparatus of claim 1 wherein said spaced portions of said load-bearing body are longitudinally spaced from one another so that changes in axial loads imposed on said load-bearing body will change the tensile forces in said load-responsive member as said spaced body portions move longitudinally in relation to one another.
 3. The load-sensing apparatus of claim 1 wherein said spaced portions of said load-bearing body are longitudinally spaced from one another and normally angularly aligned so that changes in axial loads imposed on said load-bearing body will change the tensile forces in said load-responsive member as said spaced body portions move longitudinally in relation to one another and changes in torsional loads imposed on said load-bearing body will change the tensile forces in said load-responsive member as said spaced body portions move angularly in relation to one another.
 4. The load-sensing apparatus of claim 1 wherein said measurable characteristic is an electrical property; and said transducer means include at least one strain gage mounted on said intermediate portion of said load-responsive member and exhibiting a varying range of said electrical property in response to tension variations in said load-responsive member.
 5. The load-sensing apparatus of claim 1 wherein said load-responsive member is normally tensioned to about half of its rated yield point.
 6. Apparatus adapted for sensing loads acting on a string of pipe in a well bore and comprising: a load-bearing body adapted for tandem coupling in a pipe string; an elongated load-responsive member having opposite end portions respectively secured to spaced portions of said load-bearing body for normally maintaining said load-responsive member in tension and a reduced-thickness intermediate portion adapted to deform in response to loads imposed on said load-bearing body tending to move one of said spaced body portions in relation to the other of said spaced body portions; and transducer means coupled to said reduced-thickness portion of said load-responsive member and having a measurable characteristic which varies in relation to variations in the tension in said load-responsive member occurring upon relative movement between said spaced body portions.
 7. The load-sensing apparatus of claim 6 wherein said load-responsive member is normally tensioned to about half of its rated yield point.
 8. The load-sensing apparatus of claim 6 wherein said measurable characteristic is an electrical property; and said transducer means include at least one strain gage mounted on said reduced-thickness portion of said load-responsive member and exhibiting a varying range of said electrical property in response to tension variations in said load-responsive member.
 9. The load-sensing apparatus of claim 6 wherein said opposite end portions of said load-responsive member are spaced longitudinally from one another so that changes in axial loads imposed on said load-bearing body will cause said load-responsive member to proportionally contract and elongate as such axial loads increase and decrease; and said transducer means include at least one tension-responsive strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to contraction and elongation of said load-responsive member.
 10. The load-sensing apparatus of claim 6 wherein said opposite end portions of said load-responsive member are angularly aligned and spaced longitudinally from one another so that changes in torsional loads imposed on said load-bearing body will cause said load-responsive member to proportionally twist and untwist as such torsional loads increase and decrease; and said transducer means include at least one strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to variations in the torsional forces acting on said load-responsive member.
 11. The load-sensing apparatus of claim 6 wherein said opposite end portions of said load-responsive member are angularly aligned and spaced longitudinally from one another so that changes in torsional loads imposed on said load-bearing body will cause said load-responsive member to proportionally twist and untwist as such torsional loads increase and decrease and changes in axial loads imposed on said load-bearing body will cause said load-responsive member to proportionally contract and elongate as such axial loads increase and decrease; and said transducer means include at least a first strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to variations in the torsional forces acting on said load-responsive member and at least a second strain gage mounted on said reduced-thickness portion of said load-responsive member and cooperatively arranged for responding primarily to variations in the tensile forces acting on said load-responsive member upon contraction and elongation of said load-responsive member.
 12. The load-sensing apparatus of claim 6 wherein said load-responsive member is exterior of said load-bearing body.
 13. The load-sensing apparatus of claim 12 wherein said load-responsive member is tubular and is coaxially arranged on said load-bearing body.
 14. The load-sensing apparatus of claim 12 further including: a sleeve member cooperatively arranged around said load-responsive member and having upper and lower end portions respectively extending above and below said spaced portions of said load-bearing body; first and second means respectively fluidly sealing said upper and lower end portions of said sleeve member to said load-bearing body for defining an enclosed chamber around said load-responsive member; and pressure-regulating means cooperatively arranged on said body and adapted for maintaining said enclosed chamber at an elevated pressure.
 15. The load-sensing apparatus of claim 14 wherein said load-responsive member is tubular and is coaxially arranged on said load-bearing body within said enclosed chamber.
 16. Apparatus adapted for sensing loads acting on a drill bit dependently coupled to a drill string and operatively arranged for excavating a borehole and comprising: a load-bearing body adapted for being tandemly coupled between a drill bit and a tubular drill string section and having a longitudinal bore adapted for conducting drilling fluids therebetween; a load-responsive sleeve coaxially arranged on said load-bearing body and having upper and lower end portions respectively secured rigidly to longitudinally-spaced upper and lower portions of said load-bearing body for normally maintaining said load-responsive sleeve in tension; and electrical transducer means cooperatively arranged on an unrestrained intermediate portion of said load-responsive sleeve and adapted for exhibiting a varying electrical characteristic proportional to changes in the tension in said load-responsive sleeve occurring upon variations in loads acting on said load-bearing body.
 17. The load-sensing apparatus of claim 16 further including: means on said load-responsive sleeve cooperatively arranged for concentrating strain in said unrestrained sleeve portion upon changes in the tension occurring in said load-responsive sleeve.
 18. The load-sensing apparatus of claim 16 wherein said load-responsive sleeve is exterior of said load-bearing body.
 19. The load-sensing apparatus of claim 18 further including: a tubular housing cooperatively arranged around said load-responsive sleeve; first and second means respectively fluidly sealing the upper and lower end portions of said tubular housing to said load-bearing body above and below said load-responsive sleeve for defining an enclosed chamber therearound; and pressure-equalizing means on saidd load-bearing body and cooperatively arranged for maintaining said enclosed chamber at a pressure at least about equal to the pressure in said longitudinal bore.
 20. The load-sensing apparatus of claim 16 wherein said electrical transducer means include: at least one tension-responsive strain gage mounted on said unrestrained portion of said load-responsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body.
 21. The load-sensing apparatus of claim 16 wherein said electrical transducer means include: at least one set of tension-responsive strain gages mounted on said unrestrained portion of said load-responsive sleeve and cooperatively arranged for responding to angular twisting and untwisting of said load-responsive sleeve caused by changes in torsional loads imposed on said load-bearing body.
 22. The load-sensing apparatus of claim 21 wherein said electrical transducer means further include: at least one tension-responsive strain gage mounted on said unrestrained portion of said load-responsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body.
 23. Apparatus adapted for sensing loads acting on a drill bit dependently coupled to a drill string and operatively arranged for excavating a borehole and comprising: a tubular load-bearing body having upper and lower ends respectively adapted for coupling said body in a drill string and a longitudinal bore adapted for conducting drilling fluids flowing therefrom to a drill bit coupled therebelow; a load-responsive sleeve coaxially arranged around said load-bearing body and having a reduced-thickness intermediate portion between upper and lower portions of said load-responsive sleeve; means rigidly securing said upper and lower portions of said load-responsive sleeve respectively to longitudinally-spaced portions of said load-bearing body for normally maintaining said intermediate portion of said load-responsive sleeve in tension; and electrical transducer means cooperatively arranged on said intermediate portion of said load-responsive sleeve and adapted for exhibiting a varying electrical characteristic proportional to changes in the tension in said load-responsive sleeve occurring upon variations in loads acting on said load-bearing body.
 24. The load-sensing apparatus of claim 23 wherein said electrical transducer means include: at least one tension-responsive strain gage mounted on said intermediate portion of said load-responsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body.
 25. The load-sensing apparatus of claim 23 wherein said electrical transducer means include: at least one set of tension-responsive strain gages mounted on said intermediate portion of said load-responsive sleeve and cooperatively arranged for responding to angular twisting and untwisting of said load-responsive sleeve caused by changes in torsional loads imposed on said load-bearing body.
 26. The load-sensing apparatus of claim 25 wherein said electrical transducer means further include: at least one tension-responsive strain gage mounted on said intermediate portion of said load-responsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve cauSed by changes in axial loads imposed on said load-bearing body.
 27. The load-sensing apparatus of claim 23 wherein said load-responsive sleeve is exterior of said load-bearing body.
 28. The load-sensing apparatus of claim 27 further including: a tubular housing cooperatively arranged around said load-responsive sleeve; first and second means respectively fluidly sealing the upper and lower end portions of said tubular housing to said load-bearing body above and below said load-responsive sleeve for defining an enclosed chamber therearound; and pressure-equalizing means on said load-bearing body and cooperatively arranged for maintaining said enclosed chamber at a pressure at least about equal to the pressure in said longitudinal bore.
 29. The load-sensing apparatus of claim 28 wherein said electrical transducer means include: at least one tension-responsive strain gage mounted on said intermediate portion of said load-responsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body.
 30. The load-sensing apparatus of claim 28 wherein said electrical transducer means include: at least one set of tension-responsive strain gages mounted on said intermediate portion of said load-responsive sleeve and cooperatively arranged for responding to angular twisting and untwisting of said load-responsive sleeve caused by changes in torsional loads imposed on said load-bearing body.
 31. The load-sensing apparatus of claim 30 wherein said electrical transducer means further include: at least one tension-responsive strain gage mounted on said intermediate portion of said load-responsive sleeve and cooperatively arranged for responding to contraction and elongation of said load-responsive sleeve caused by changes in axial loads imposed on said load-bearing body. 